The present invention relates to a process and apparatus for the anaerobic treatment of municipal or industrial waste water with the simultaneous production of biogas, e.g. methane, carbon dioxide, etc. More particularly, the present invention relates to such a treatment process and apparatus by which the waste water is subjected to the action of anaerobic micro-organisms in a filter containing a granular filler material to which the resultant biomass attaches itself. A number of systems of this general type are known, in which known systems the waste water to be treated is passed from bottom to top or from top to bottom of an anaerobic filter material which is to be filled with a stationary or movable supporting material. Several types of systems are known in which the supporting material is stationary. The material can be immersed and passed from top to bottom by the water which is to be treated. The treatment time therefore is very short and requires a high return rate. The supporting material can be immersed, with the water to be treated circulating from top to bottom or from bottom to top. If an orderly supporting material is used, e.g. a plastic material, such material has a small specific surface, so that only a small quantity of biomass can attach itself thereto. Also, problems arise concerning the distribution of the water to be treated and the recirculated water. If a loosely packed or granular material is used (e.g. clay, flint), there is a serious risk of clogging the filter, the biomass having a tendency to grow and to block the free flow of water, and the water flow rate being too low to tear away the excess biomass.
Systems also are known in which the supporting material is, for example, movable, expanded or fluidized by the water to be treated and by the recirculated water. However, in this type of system there is the risk of clogging the devices which feed such fluids, and there are serious problems regarding the spreading of the water to be treated and of the circulated water. In addition, some of these known systems require settling of the treated water outside the filter itself.